1. Field of the Invention
The present invention relates to a hearing device, in particular a hearing aid, of the type having a data transmission unit to receive a synchronization signal and an oscillator unit to clock the data transmission unit.
2. Description of the Prior Art
There is generally a need for fast and wireless data transmission to and from hearing aids, i.e., to and from the audio signal processing circuit therein. It should be possible to provide all hearing aid types from the large BTE (behind-the-ear) hearing aids through ITE (in-the-ear) hearing aids to the smallest CIC (Completely In the Channel) hearing aids with fast data transmission. The multi-value modulation techniques (QAM, QPSK) necessary for this however require the transmitter and receiver oscillator frequencies to correspond to an accuracy of <+/−0.1%.
The data speeds that have been possible to achieve heretofore without frequency-stable components are around 100 bit/s for transmissions known as ear-to-ear connections. Higher data speeds require frequency-stable components such as quartzes, SAW (Surface Acoustic Wave components), ceramic resonators or micro-electromechanical structures (MEMS). The audio data is then generally transmitted to supplementary hearing aid adapters. In the case of ITE or CIC hearing aids there are currently no solutions with a high data speed (>40 kbit/s).
U.S. Pat. No. 6,839,447 describes radio transmission methods (DSSS, FHSS), which are used in commercial radio networks (GSM, DECT, WLAN, Bluetooth), and demonstrates corresponding hearing aid applications. A technique known as “clock retrieving” is described specifically there, where the symbol clock is restored for the synchronous transfer of the demodulated data. An “RF carrier recovery” method is also presented, according to which a carrier frequency is restored, e.g. for coherent demodulation. These methods only function reliably, however, only if a stable basic clock pulse is already available in the hearing aid. Otherwise the synchronization of two independent hearing aids would be extremely unreliable and susceptible to faults. Therefore the frequency-stable components described above, such as quartzes, are generally used. This is even more the case for frequency bands in the region of more than 200 MHz. The frequency-stable components used, however, have the disadvantage of high power consumption and large bulk, which is unacceptable for ITE hearing aids in particular.